The Experimental Immunology Branch (EIB) Flow Cytometry Core Facility currently supports multiple research projects for more than 50 investigators from within the EIB and elsewhere in the Center for Cancer Research (CCR). These investigations involve multiparametric quantitative single cell analysis of, and electronic cell separation based upon, parameters associated with cells freshly prepared from different species and/or tissues, as well as a spectrum of in vitro cultured cells. Basic research support is provided to members of the EIB and to other investigators within the Center for Cancer Research, NCI. Currently supported projects include, but are not limited to, the following areas of study: a) in vivo and in vitro analyses of intra-cellular signaling via cell surface molecules; b) analyses of cellular processes and/or defects in animals and/or cells with genetic modifications; c) studies of the mechanisms and consequences of immune pathogenesis; d) analyses of the coordinate cell surface expression of a variety of molecules; e) investigations of T cell repertoire generation; g) analyses of expression of transplantation antigens; h) investigations of mechanisms involved in T cell lineage development; i) mechanisms of cell death; and j) stem cell analyses. The facility operates and maintains 2 operator run 3-laser flow cytometers with cell sorting capabilities and 3 user-operator flow cytometers with analysis only capabilities. The facility has recently acquired a state-of-the-art 5-laser, analysis only, flow cytometer that will be used to extend and expand available applications. Facility staff provide consultation to investigators in the areas of: experimental design, problem-solving, reagent selection and data analysis and interpretation. The facility supports a wide variety of flow cytometric applications including: rare event analysis (including stem cell analysis) and cell sorting; multi-color phenotypic analyses, cell cycle analysis, proliferation analysis, metabolic analyses including calcium flux analysis, sterile cell sorting, and intra-cellular cytokine analyses. The facility also, as a cost-savings measure, maintains a reagent bank of over 150 commonly used flow cytometry reagents that are pre-titred and aliquoted by facility personnel for use by multiple EIB investigators. The reagent bank minimizes costs by buying in bulk and minimizing labor and effort involved in characterizing individual batches of reagents. The facility is developing WINDOWS-based pc software for flow cytometry analysis that will provide capabilities not currently available in software available from instrument manufacturers or 3rd party software sources.